phrase used to describe disbelief. (It is important to pronounce the two syllables of "reckon" distinctly, with the emphasis on the second syllable. In its most glorious form, it is used by school boys interspersed with the vile gesture of pouting the bottom lip while tightening the skin between there and the chin, and then flicking the tip of the tongue back and forth against the flesh just above the lower front teeth. It makes a grotesque noise, and is so obnoxious that - at least when I was at school - as good as guaranteed a fight.)
You met Michael Jordan and played him at one on one and won, did you? Yeah! Chinny reckon, you did.
Definitions include: to engage in an activity which is inherently wasteful (particularly when one is at work) and for which there isn't any tangible compensation or reward, other than one's own mental stimulation.